Boise,ID –

Boise fire and police investigators have determined that an accidental natural gas leak caused the explosion at a home on 6th Street Monday morning.

The gas leak apparently came from an unused gas line that had been capped. The valve had come open, causing the leak, police said.

The early morning explosion sent two men to a burn center in Salt Lake City for treatment of burns to their hands, arms and faces, and did considerable damage to the small home on 6th Street. As of Monday night, there was no further update on the conditions of two men sent to a Salt Lake City burn unit, police said.

Boise firefighters were called at 4:18 a.m. to investigate an explosion at a house in the 1600 block of North 6th Street, between Alturas and Sherman.

Four people, all 20-somethings, were at the house before the explosion, according to Boise Fire Battalion Chief J.D. Ellis. They were awakened by an odor, he said.

Initial reports about the explosion were that two of the four people at the house stayed inside, and those two were burned. Fire Department spokeswoman Lynn Hightower said that investigators later learned that all four were in the house.

The two men who were injured in the explosion were in the utility room at the rear of the house when the explosion occurred. The two others, a man and a woman, were in the front of the house.

The explosion did not cause a fire inside the house.

Ellis said a police officer who was first on scene noted the odor of rotten eggs, similar to the odor that is given to natural gas so residents can easily detect leaks. The house has natural gas service, and Intermountain Gas is on scene.

The damage to the house was extensive. The blast not only blew out the back wall, but also blew out the front windows and caused a partial roof collapse.

Cooper, a 5-year-old chocolate lab that was in the house at the time of the explosion, wandered off after firefighters brought him outside. Police found the dog in the Foothills at about 11 a.m.